Graham bemethavinci
If your gonna use a template then bootstrap is the most widely used has the most tutorials and is actually quite simple to use once you understand the basics

foundation is very similar but is aimed a little more at professionals with a private server

W3css is in theory the most simple and has a lot more preset colors but you have to add a lot of the js and jquery as you go which means in some ways it is more complicated

which ever of them you choose you either need to use twig for the blog / forum or create your own styles in a separate style sheet as the classes do not match

If you want real simplicity then as I said just go for one of the xtgem templates and use a un twigged blog/forum

to be honest a good site is more about the quality of original content that you add then it is about all the frilly gimmicks

if you want to build your own from the bottom up then you have to do all that work yourself and that is probably the hardest option as it is like learning to speak several foreign languages and can take years of study